The present invention relates to impedance transforming elements, and in particular to an integrated broadside coupled transmission line element.
The use of twisted pairs of copper wires to form coupled transmission line elements is well known. These transmission line elements may be used to create baluns, balanced and unbalanced transformers and current and voltage inverters. Examples of the use of conventional transmission line elements are presented in C. L. Ruthroff, xe2x80x9cSome Broad-Band Transformers,xe2x80x9d Proceedings of the IRE (Institute for Radio Engineers), vol. 47, pp. 1337-1342 (August 1959), which is incorporated herein by reference. These transmission line elements are typically found in forms that are useful in frequency bands through UHF.
The use of such transmission line elements in integrated circuits such as RF power amplifiers and low noise amplifiers that operate at higher frequencies is desirable. However, the incorporation of numerous off-chip devices such as these conventional transmission line elements into RF devices such as cellular telephones is not competitive due to size and cost. Moreover, conventional coupled transmission line elements are not suitable for use in the desired frequency range.
Therefore, a need has arisen for a coupled transmission line element that addresses the disadvantages and deficiencies of the prior art. In particular, a need has arisen for a integrated broadside-coupled transmission line element.
Accordingly, a novel broadside-coupled transmission line element is disclosed. In one embodiment, the element includes a first metallization layer that has a first spiral-shaped transmission line and at least one bridge segment formed therein. The element also includes a second metallization layer that has a second spiral-shaped transmission line and connector segments formed therein. The connector segments provide respective conduction paths between the inner area of the first and second transmission lines and the outer area of the first and second transmission lines. A first one of the connector segments is electrically connected to the inner terminus of the second transmission line. The second transmission line has a gap at each intersection with the connector segments. A dielectric layer lies between the first and second metallization layers. The dielectric layer has a plurality of apertures formed therein for providing electrical connections between the second transmission line and the bridge segment(s) of the first metallization layer, and for providing an electrical connection between the inner terminus of the first transmission line and a second one of the connector segments.
An advantage of the present invention is that a coupled transmission line element may be realized in an integrated circuit environment. Another advantage of the present invention is that the element may be used to create various circuit elements such as baluns, balanced and unbalanced transformers, power splitters, combiners, directional couplers and current and voltage inverters. Yet another advantage is that the element may be used at higher signal frequencies than conventional non-integrated coupled transmission line elements.